//
// Copyright (c) 2020 Hiroshi Kimura(Muukii) <muukii.app@gmail.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import Foundation

public final class Scan<Element, Accumulate> {

  public typealias Accumulator = (inout Accumulate, Element) -> Void

  public var value: Accumulate {
    _value.value
  }

  private let _value: VergeConcurrency.UnfairLockAtomic<Accumulate>
  private let _accumulator: Accumulator

  public init(seed: Accumulate, accumulator: @escaping Accumulator) {
    self._value = .init(seed)
    self._accumulator = accumulator
  }

  public func accumulate(_ element: Element) -> Accumulate {
    _value.modify { _v -> Accumulate in
      _accumulator(&_v, element)
      return _v
    }
  }

}

extension Scan {

  /// A Scan instance that increments itself integer value each event received
  public static func counter() -> Scan<Element, Int> {
    .init(seed: 0, accumulator: { n, _ in n += 1 })
  }

}
